全文获取类型
收费全文 | 3757篇 |
免费 | 369篇 |
出版年
2021年 | 52篇 |
2019年 | 41篇 |
2018年 | 44篇 |
2017年 | 42篇 |
2016年 | 60篇 |
2015年 | 123篇 |
2014年 | 106篇 |
2013年 | 142篇 |
2012年 | 231篇 |
2011年 | 239篇 |
2010年 | 138篇 |
2009年 | 136篇 |
2008年 | 203篇 |
2007年 | 227篇 |
2006年 | 233篇 |
2005年 | 197篇 |
2004年 | 227篇 |
2003年 | 196篇 |
2002年 | 195篇 |
2001年 | 45篇 |
2000年 | 27篇 |
1999年 | 38篇 |
1998年 | 50篇 |
1997年 | 43篇 |
1996年 | 46篇 |
1995年 | 36篇 |
1994年 | 48篇 |
1993年 | 30篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 42篇 |
1983年 | 31篇 |
1982年 | 51篇 |
1981年 | 40篇 |
1980年 | 37篇 |
1979年 | 31篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1975年 | 29篇 |
1974年 | 26篇 |
1973年 | 29篇 |
1971年 | 19篇 |
1969年 | 20篇 |
1968年 | 19篇 |
排序方式: 共有4126条查询结果,搜索用时 15 毫秒
121.
Leaf pocket resins of 11 species of the tropical arborescent genus Hymenaea are virtually identical qualitatively, but of widely varying quantitative proportions. Within this large range of variability, several strong positive quantitative correlations between resin constituents were found, especially between caryophyllene and β-humulene and between γ-muurolene and δ-cadinene. These data lead to clarification of sesquiterpene biosynthetic routes in Hymenaea. In addition, quantitative relationships found among caryophyllene, α- and β-selinene, γ-muurolene and δ-cadinene are explained only with difficulty by long accepted biosynthetic pathways, and the intermediacy of germacrenes is suggested. 相似文献
122.
123.
Don B. Destephano U. Eugene Brady Leesa B. Woodall 《Prostaglandins & other lipid mediators》1976,11(2):261-273
An active prostaglandin (PG) synthetase was found in the 12100 g pellet of reproductive tract homogenates of the male house cricket, . Comparatively, the 12100 g supernatant and the microsomal fractions were inactive. The PG synthetase in the pellet fraction was characterized in terms of cofactor, temperature, pH, and incubation time requirements. Indomethacin, a known inhibitor of mammalian PG synthetase, was not inhibitory to the cricket synthetase. The procedure and findings are relevant to PG synthetase studies of any organism or tissue. 相似文献
124.
The effect of selected inhibitors on the thrombin-stimulated burst and the basal oxygen consumption of washed human platelets were investigated and compared with inhibition of the release reaction. Cyanide (0.2 mM) caused complete inhibition of the basal respiration, but only 15% inhibition of the thrombin-stimulated burst of oxygen consumption. Similar differential inhibitory effects were observed with oligomycin, antimycin, rotenone and N-ethylmaleimide. Prostaglandin E1 (0.03 mM) and acetylsalicylic acid (0.8 mM) had little effect on basal respiration, but inhibited the thrombin-stimulated burst of oxygen consumption. N-Ethylmaleimide (0.4 mM) inhibited the release of calcium from platelets by 90%, while prostaglandin E1, acetylsalicylic acid and the above mitochondrial inhibitors caused no more than 30% inhibition of the release reaction. Our results provide evidence that basal respiration and a portion of the thrombin-stimulated burst of oxygen consumption are involved in respiratory chain phosphorylation, and that this component of the thrombin-stimulated burst may be coupled to the maintenance of the release reaction. 相似文献
125.
Summary Cylindrical shells of potato tissue were slid around the bulb of a thermometer and subcooled. Attempt was then made to induce crystallization by tapping the upper end of the thermometer. Out of 122 trials 52 were successful. In a few experiments, 15 repeated taps were ineffective. There is absolute evidence of the efficacy of tapping in some cases and of its inefficacy in others.The percentage of successful tappings increases at lower temperatures but since the percentage of spontaneous crystallizations also increases, a much larger number of determinations would be necessary to derive a relation between degree of subcooling and efficacy of tapping.No evidence was found in these experiments of the existence of discontinuous zones of lability at various degrees of subcooling. 相似文献
126.
127.
We examined Cortisol (F) dynamics in female baboons treated with diethylstilbestrol (DES) or estradiol (E2) and compared values with those previously measured in nonpregnant and pregnant animals. Five regularly menstruating baboons (12–18 kg, BW) were administered 5 mg DES daily via fruit or 0.5 mg E2/0.1ml oil sc for 30 days. Blood samples, obtained before and after treatment, were assayed for serum F concentrations and serum Cortisol binding capacity (CBC). The metabolic clearance (MCR) and production rate (PR) of F and the catabolism of i.v. administered [3H] F were examined 25 and 30 days after initiation of estrogen treatment. Compared with values in nonpregnant baboons, F metabolism in estrogen treated animals is significantly altered and is characterized by increased formation of unconjugated metabolites, decreased glucuronylation, increased excretion of unconjugated F, cortisone, and highly polar metabolites, and increased CBC. These changes induced by estrogen are similar to those observed in intact pregnant baboons and permit the suggestion that the pattern of F metabolism and the level of CBC in baboon pregnancy are the result of elevated estrogen production.However, estrogen also caused a significant decrease in the MCR and PR of F, parameters which, by contrast, are similar in intact pregnant and nonpregnant baboons. These findings indicate that while estrogen also influences the rate of F clearance and F production, these effects of estrogen are not apparent during pregnancy. Collectively, these findings allow the suggestion that estrogen is a major factor which alters F metabolism and increases serum CBC in baboon gestation. However, additional factors are operative in primate pregnancy which maintain PR and MCR of F at levels similar to those of nonpregnant baboons. 相似文献
128.
129.
In two previous papers Giles, Walsh and Bradley ('66) and Giles, Wyber and Walsh ('70) have shown that the inhabitants of three adjacent villages on the edge of the Markham Valley in New Guinea have significant heterogeneity in all blood group frequencies tested. The language, environment, culture, and ancestry of these people are essentially identical. The differences in the blood group frequencies were attributed to genetic drift and particularly to founder effect. In this paper the anthropometric data from these villages are analysed. Analysis of variance shows that 50% of the traits are significantly different. Multiple discriminant analysis demonstrates that the villages can be significantly separated morphologically. The heritability of each trait is determined using an analysis of within and among sibship variation. Traits with strong “genetic” components of variation and traits with strong “environmental” components contribute significantly to the morphological heterogeneity among the villages. Some speculations are presented on the cause of the “genetic” component of morphological variation. 相似文献
130.